The purpose of this proposal is to provide access to a reliable, state-of- the-art X-band CW EPR spectrometer with high sensitivity and time resolution at the Biophysics Research Institute of the Medical College of Wisconsin. Each of these projects employs EPR as the primary analytical tool. The requested instrument will allow the faculty to pursue their NIH-funded projects with a rigor not otherwise possible. Specifically, the projects that will benefit include (1) characterization of ligand-induced conformational changes in the ferric enterobactin receptor as studied by site-directed spin labeling, (2) studies of oxidation/nitration by nitric oxide, (3) reactions between nitric oxide, peroxynitrite, and thiols, (4) analysis of free radical mechanisms of LDL oxidation, (S) examination of endothelial nitric oxide synthase and the radical mechanism of antitumor anthracyclines, (6) EPR studies of the antitumor agent bleomycin and its complexes with DNA, (7) spin label oximetry investigations, (8) studies of the molecular basis of lens transparency, and (9) site-directed spin labeling studies of small heat- shock proteins. Each of these projects has a clear need for increased access to a research-level EPR spectrometer. This proposal seeks funding for an instrument with high sensitivity, accurate temperature control in the range of 4 - 400 K, well-developed and adaptable software, and time resolution on the order of a few milliseconds. EPR is a fundamental technique in studies of protein and metalloprotein structure and in elucidating free radical intermediates in biochemical and pathological processes. Investment in the requested spectrometer will substantially strengthen NIH-supported research.